September 5, 2013

Biggest Volcano On Earth At Bottom Of Pacific

Researchers, led by University of Houston professor William Sager, have been able to confirm the existence of the world’s largest single volcano at the bottom of the Pacific Ocean, according to an upcoming report in Nature Geoscience.

Called Tamu Massif, the volcano covers an area about the size of the British Isles. Without a similar volcano here on Earth, scientists are comparing to it giant volcanoes on Mars and ranking it among the biggest known in the Solar System.

"Tamu Massif is the biggest single shield volcano ever discovered on Earth," Sager said. "There may be larger volcanoes, because there are bigger igneous features out there such as the Ontong Java Plateau, but we don't know if these features are one volcano or complexes of volcanoes."

The volcano sits 1,000 miles east of Japan and is the largest feature of Shatsky Rise, an underwater mountain range created 130 to 145 million years ago by the eruptions of numerous underwater volcanoes. Until this latest report, scientists hadn’t been able to confirm whether Tamu Massif was a single volcano or was comprised of several eruption points.

Using core samples taken from the ocean floor, the authors have been able to confirm that the basalt rock constituting Tamu Massif did in fact come from a single source. The samples were taken from several locations on Tamu Massif, and seismic data from a series of scientific cruises over the area showed the structure of the volcano, confirming that the lava flowed hundreds of miles downhill into adjacent basins on the ocean floor.

The massive volcano is also highly unique because of its low, broad shape. The volcano’s flatness suggests that its lava flowed great distances compared to most other volcanoes on the planet. The seafloor is sprinkled with thousands of underwater volcanoes that are much smaller and steeper than Tamu Massif.

"It's not high, but very wide, so the flank slopes are very gradual," Sager said. "In fact, if you were standing on its flank, you would have trouble telling which way is downhill.”

“We know that it is a single immense volcano constructed from massive lava flows that emanated from the center of the volcano to form a broad, shield-like shape,” he added. “Before now, we didn't know this because oceanic plateaus are huge features hidden beneath the sea. They have found a good place to hide."

Tamu Massif covers about 120,000 square miles, much larger that Hawaii's Mauna Loa – the largest active volcano on Earth – which covers about 2,000 square miles. A much better analog would be Olympus Mons on the planet Mars, which is about 25 percent bigger by volume than Tamu Massif.

The research team estimated Tamu Massif’s age at around 145 million years old. Sitting about 6,500 feet below the ocean surface, the researchers said the volcano became dormant within a few million years after being formed.

"It's shape is different from any other sub-marine volcano found on Earth, and it's very possible it can give us some clues about how massive volcanoes can form," Sager said. "An immense amount of magma came from the center, and this magma had to have come from the Earth's mantle. So this is important information for geologists trying to understand how the Earth's interior works."